And God said, let Us make man in Our image, according to Our likeness; and let them rule over the fish of the sea, and over the birds of the heavens, and over the cattle, and over all the earth, and over all the creepers creeping on the earth. And God created the man in His own image; in the image of God He created him. He created them male and female. Gen 1:26-27
When man was created, man was a joint entity. The one man was created as both male and female. Both having been in the one body, they were a unity, echad. As that, we can understand more about the verse that follows the creation of the woman.
Therefore, a man shall leave his father and his mother, and shall cleave to his wife and they shall become one flesh. Gen 2:24
Although both are now separate creatures, there is still this built in desire to be as one, to share in life as a singleness, to have and to hold the other. Perhaps that is why hugging and cuddling is so important in a relationship. At those moments, we can again relive the unity that once was, back at the time of creation.
Barukh atah Adonai Elohenu Melekh HaOlam
Blessed are you, Oh L-rd our G-d, Ruler of the Universe